isl: Handle MOD_INVALID in clear color plane check

In iris, if whandle->modifier is DRM_FORMAT_MOD_INVALID within
iris_resource_from_handle, isl_drm_modifier_plane_is_clear_color will
assert fail on non-existent modifier info. Update that function to
return early instead.

Fixes the assert failure when running the piglit test case:

   ext_image_dma_buf_import-sample_yuv -fmt=YVYU -auto

   ext_image_dma_buf_import-sample_yuv: ../../src/intel/isl/isl.h:2352:
      isl_drm_modifier_plane_is_clear_color: Assertion `mod_info' failed.

Fixes: 81d132d5ea ("iris: Use helpers for generic aux plane importing")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26826>

src/intel/isl/isl.h

@@ -2347,6 +2347,9 @@ isl_drm_modifier_has_aux(uint64_t modifier)
 static inline bool
 isl_drm_modifier_plane_is_clear_color(uint64_t modifier, uint32_t plane)
 {
+   if (modifier == DRM_FORMAT_MOD_INVALID)
+      return false;
+
    ASSERTED const struct isl_drm_modifier_info *mod_info =
       isl_drm_modifier_get_info(modifier);
    assert(mod_info);